This invention relates generally to the translocation of metabolites in a growing stem and more particularly to a method and device for bringing about the effects of girdling by mechanical means.
Girdling is variously defined, the term referring generally to encircling a stem partially or completely by a cut, commonly through the bark, at times into the wood, to interrupt pathways for translocation of metabolites. Girdling techniques have been used for centuries. To induce earlier fruiting in a tree slow to produce, a grower may girdle the tree by removing a band of bark of a predetermined width from the entire circumference of the trunk. This is called ringing. A stem may be girdled completely around by one knife or saw cut through the bark to enhance the size and number of fruit. This is called scoring. Notching is a technique whereby bark in only a small portion of the circumference is interrupted, as above a bud, to induce growth by blocking suppressive hormones from the distal growing tip. These injuries heal generally in the course of one or two seasons. In clearing a forest, the woodsman may kill a tree by cutting deeply into the wood around the trunk.
The above techniques have in common the immediate development of insufficiency of media for translocation of metabolites by interruption of these pathways, generally in the phloem, sometime in the wood.
Carbon dioxide and water are combined by photosynthesis in the green leaves of a plant to form carbohydrates, the building material of roots, stems, flowers, leaves, fruits and seeds. Carbohydrates move from the leaves, through the bark generally downward toward the roots. Water and minerals absorbed by the roots move generally upward through the wood, deep to the bark, toward the leafy extremities, with the more superficial layers of wood carrying a disproportionately larger amount of water and minerals than the deeper layers. In a stem of a growing plant, new wood is formed deep to the cambium, superficial to other wood already formed, the cambium with overlying bark being thrust thereby outwardly, or centrifugally. New bark is formed superficial to the cambium. The radius and circumference of the stem increase concomitantly, so that growth may be resolved into two components, radial and circumferential. A strong band closely encircling a growing stem will oppose these components and the bark, while being compressed against the inner surface of such a band by the underlying growth, will be progressively compressed and translocation through it impeded. No new wood will be formed beneath the band. Translocation in the superficial wood already present will decrease with age. Strangulation will ultimately ensue. Encircling bands and rings of wire have been applied to stems in attempts at enhancing formation of pollen and flowers, with some degree of success. Related experimentation has included girdling, with removal of a completely encircling strip of bark at one level, with semicircular girdling cut at each of two levels, with a spiral gridling cut extending beyond one level and occupying all sectors about the stem axis, and girdling cuts at one level occupying more than 180.degree. about the axis of the related stem. The method of this invention allows for accomplishing the ends of these prior methods with minimal if any bark injury, with no exposure of wood to dessication and invasion, and for the elective use of a slot for containment of growth, advantages not attainable with the other methods. A girdling cut is frequently overgrown in two or three seasons. Such has not been observed so far in the application of this method. With the arrangements most widely used it is physically impossible. The method thus provides an elective permanency of effect contingent on the lengths of applied slots.